EXFO FTB -5240S/5240BP Optical Spectrum Analyzer - Manual (Page 88)

Setting Up the Instrument in WDM Mode
82 FTB-5240S/S-P/BP
Using the Commissioning Assistant
Using the Commissioning Assistant
If you have purchased the commissioning (Com) option, you can use an
assistant to calculate the OSNR of coherent channels.
The assistant lets you select a measurement file where all channels are on,
or active, and then compares them to other measurement files on which
one of the channels is off while all of the others are still on.
The commissioning assistant automates OSNR measurements of
40 G/100 G coherent signals based on two standards: the China
Communications Standards Association (CCSA) YD/T 2147-2010 and the
IEC recommendation 61282-10 (draft).
The Chinese CCSA YD/T 2147-2010 standard recommends calculating
Pol-Mux OSNR as follows:
where, for a 50 GHz channel:

P is the integrated power (Signal + Noise) over the 0.4 nm channel
bandwidth

N is the integrated power (Noise) over 0.4 nm bandwidth

n is the integrated power (Noise) inside 0.2 nm, then normalized to
0.1 nm
Pol Mux OSNR 10log
10
P N –   n 2       =